Multiple-spool control valves generally comprise a plurality of directional control valve sections, each provided with a shiftable control spool controlling fluid flow to one or more hydraulic actuators. The valve sections are sandwiched between inlet and outlet end sections having ports connectable with a source of fluid and a low pressure reservoir. Open-center type assemblies permit continuous open-center flow transversely through the valve assembly from the inlet to the outlet when all the spools are in neutral non-operative positions. Upon shifting a control spool to divert the fluid to actuate the associated actuator, the spool variably restricts or shuts off the open-center flow.
Pressure drop across a valve assembly as fluid flows through the valve is associated with power loss. An improved design that reduces pressure drop may thus be desirable.
In examples, the valve assembly may be placed on a vehicle to control various actuators of the vehicle. Various hoses and plumbing components are connected to the various valve sections. Orientation of the workports of the valve assembly that are connected to the actuators affects the complexity of plumbing and thus affects reliability and failure rates. Thus, orientating the workports in a particular direction may reduce complexity of plumbing. However, such change in orientation of workports affects layout of fluid passages and coring design inside the valve sections.
Another concern with spool valves involves spool bore distortion. Valve sections may have longitudinal bores therein to accommodate spools that are shiftable in the bores. When high pressure fluid flows through the internal passages of the valve section, the longitudinal bore that accommodates the spool may be distorted under pressure. Such distortion may cause the spool to bind and may thus hinder actuation of the spool. It may thus be desirable to design the valve sections and layout of internal passages in a manner that reduces impact of high pressure fluid on internal walls of the valve section so as to reduce distortion.
In examples, valve sections are equipped with pressure relief valves that are normally closed, but are configured to open a fluid path to a reservoir when pressure level associated with a given workport exceeds a predetermined pressure value. In this manner, the actuators controlled by the valve assembly are protected from high pressure levels that could cause damage. In examples, a respective relief valve is associated with each workport. For instance, if there are two workports in each valve section communicating fluid to and from respective chambers of a hydraulic actuator, two relief valves are installed in the valve, one relief valve for each workport. Having a relief valve for each workport is costly, and it may thus be desirable to have a single relief valve protecting both chambers of the actuators.